Iodothyronine deiodinases in a mammalian hibernator, the chipmunk (Tamias asiaticus).
We examined the activities of iodothyronine deiodinase, a key enzyme for thyroid hormone metabolism, in selected tissues of the chipmunk (Tamias asiaticus), a mammalian hibernator, of both sexes in the summer season. Reverse T3 5'-deiodinase (5'-D) activity was the highest in the liver followed by the kidney; T4 5'-D activity was the highest in brown adipose tissue (BAT) and T3 5'-deiodinase (5-D) activity was the highest in the testes followed by the brain. Distributions of three types of deiodinase activities in liver kidney BAT, and brain were comparable to other mammals reported, except that the type III deiodinase was unique in testes. The 5'-D activity of liver and kidney of chipmunks was 52% and 24%, respectively, of male rats and the 5-D activity of brain and testes of chipmunks was 227% and 567%, respectively of male rats. In addition, the cold exposure increased BAT 5'-D activity in chipmunks as reported in the ground squirrels. Our results indicated that tissue distribution of deiodinases and response to cold exposure in BAT in hibernators are similar to nonhibernators. However, there was a quantitative difference of rT3 5'-D and T3 5-D activities in some tissues between chipmunks and rats, indicating different local thyroid hormone metabolisms in hibernators and nonhibernators.
Ohba
K
K
Department of Pharmacology, Tokyo Women's Medical College, Tokyo, Japan. kohba@research.twmc.ac.jp
Tsukahara
F
F
Uchida
Y
Y
Ogawa
A
A
Muraki
T
T
D002001:Adipose Tissue, Brown / Q000201:enzymology; D000818:Animals; D001921:Brain / Q000201:enzymology; D003080:Cold Temperature; D005260:Female; D006605:Hibernation; D007453:Iodide Peroxidase / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008297:Male; D012589:Sciuridae / Q000378:metabolism*; D012621:Seasons
D007453:Iodide Peroxidase